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Raksha Urs, Jeffrey Ketterling, D Jackson Coleman, Ronald Silverman; Ultrasound Characterization of Blood-Flow in the Choroid and Retina. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4826.
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To image and measure flow-velocity and perfusion in the choroid and retina using a recently developed linear-array based ultrasound technique, coherent compound plane-wave imaging (CCPWI).
We programmed a research ultrasound platform (Verasonics Vantage 128) to perform CCPWI using a 20 MHz linear array. B-mode images of the posterior pole were acquired at 15,000 images/s. 15 images were acquired over ±15ο to form 1000 compound images/s by coherent addition. Images were acquired for 2.25 seconds to capture 2-3 cardiac cycles. We developed methods to visualize slow-flow in the retinal-choroidal region offline and produce power Doppler images. We measured blood flow over the entire visualized retina-choroidal region using short-time Fourier transform and obtained spatially averaged mean velocity. Perfusion was measured as the integral of the power Doppler signal. Retinal-choroidal perfusion was characterized as a function of time. The peak frequency of perfusion variation (corresponding to the heart rate) was extracted and the Fourier-component corresponding to that frequency summed with the DC component was used to model perfusion variation. Power Doppler Index (PDI) was calculated from the model as (PDMax - PDMin)/PDMax. To demonstrate this technique, we acquired two sets of images each, before and at 1 and 2 hours after intake of 40 mg sildenafil, a medication believed to cause dilation of retinal/choroidal vessels. Experiments were performed on one subject on three separate days.
Paired t-tests revealed all measurements were significantly different before and after sildenafil intake. Mean pre-treatment velocity was measured as 11.72±0.99 mm/s, decreasing to 10.39±1.99 mm/s (-11%; p=0.08) at 1 hour post sildenafil intake, and 10.03±1.76 mm/s (-14%; p=0.02) at 2 hours. Normal PDI was 0.40±0.06 but increased to 0.55±0.19 (+36%; p=0.03) at 1 hour post sildenafil and 0.48±0.1 (+23%; p=0.01) at 2 hours.
Ultrasound CCPWI presents a novel method of determining flow velocity and perfusion in the retinal-choroidal region. We foresee immediate research and clinical applications of this method in the evaluation of conditions influencing retinal and choroidal flow, such as glaucoma and macular degeneration.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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